Breaker and Bus bar ratings
Breaker and Bus bar ratings
(OP)
Dear Folks,
Pl. advice me for breaker and Switchgear ratings.
We have 9-AC generators are connected in parallel without grid supply. All neutrals are solidly grounded without neutral breaking during parallel operation. Fault levels are calculated by ETAP software and these values are as follows.
ANSI calculations (Device duty- 3ph):
Fault currents on Main Bus:
Interrupting Duty: 156.506kA symmetrical rms
Momentary Duty:245kA Assymmetrical kA rms & 410.080kA Assymetrical kA crest.
Steady state current:56kA rms (calculated manually)
Based on the above values, pl. advice for switchgear outgoing breakers MAKING AND BREAKING CAPACITY, SHORT CIRCUIT WITH-STAND CURRENT for 1-sec and Switchgear BRACING CURRENT & SHORT-CIRCUIT WITHSTAND CURRENT for 1-sec.
Advanced thanks for your replies and discussion.
Pl. advice me for breaker and Switchgear ratings.
We have 9-AC generators are connected in parallel without grid supply. All neutrals are solidly grounded without neutral breaking during parallel operation. Fault levels are calculated by ETAP software and these values are as follows.
ANSI calculations (Device duty- 3ph):
Fault currents on Main Bus:
Interrupting Duty: 156.506kA symmetrical rms
Momentary Duty:245kA Assymmetrical kA rms & 410.080kA Assymetrical kA crest.
Steady state current:56kA rms (calculated manually)
Based on the above values, pl. advice for switchgear outgoing breakers MAKING AND BREAKING CAPACITY, SHORT CIRCUIT WITH-STAND CURRENT for 1-sec and Switchgear BRACING CURRENT & SHORT-CIRCUIT WITHSTAND CURRENT for 1-sec.
Advanced thanks for your replies and discussion.






RE: Breaker and Bus bar ratings
AC generators- 6no.s
Rating: 1312kVA, 400V, 60HZ, 0.8pf, 1800 rpm
Xd:2.68 p.u
X2:0.187 pu
X0:0.0161 pu
X"d:0.101 pu
X'd:0.127 pu
Other AC generators- 3no.
Rating: 1031 kVA, 400V, 60HZ, 0.8pf, 1800 rpm
Xd:2.29 p.u
X2:0.183 pu
X0:0.054 pu
X"d:0.026 pu
X'd:0.13 pu
Total 9-generators are conencted to common switchgear without any intermediate transformers.
RE: Breaker and Bus bar ratings
I'm curious about your 400V, 60Hz as 400V is usually a 50Hz voltage rather than a 60Hz voltage.
RE: Breaker and Bus bar ratings
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If we learn from our mistakes I'm getting a great education!
RE: Breaker and Bus bar ratings
But still I am more concern about Switchgear for fault levels. If not possible, I would like to propose the loads to divide into two switchgear units.
Project is already finalised and purchage orders released with low fault levels (75kA/1sec short-time withstand rating) and it came to us for review.
What is best option at this stage?
Devide the loads in to two switchgears and distribute the generators into these two switchgears.
or
Provide fault limiting reactors
Advanced thanks for your reply.
RE: Breaker and Bus bar ratings
RE: Breaker and Bus bar ratings
a) Fire the designer.
b) Sue the designer.
Split the load down into smaller blocks. It sounds like your switchgear is under-rated for the application unless you can get split in to three lumps. How did this mess occur?
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If we learn from our mistakes I'm getting a great education!
RE: Breaker and Bus bar ratings
Scotty, nice options
Regards.
Slava